The invention relates to a circuit arrangement for wirelessly exchanging data with a reader device, comprising an antenna for converting electromagnetic radiation into an antenna voltage, an analogue circuit for demodulating of an information signal based on the antenna voltage, a digital circuit for processing of the information signal, and a decoupling circuit interconnecting the analogue circuit and the digital circuit. The invention also relates to RFID chip card devices.
So-called RFID chip cards comprise antennas, whose antenna voltage serve two purposes, for transmitting data between a reader device and the RFID card, and for supplying energy to further components of the RFID card.
Because contactless chip cards do not comprise a power supply unit of their own, they can be manufactured particularly cheap and are thus suited for a variety of applications. Systems, which require the use of a multiplicity of chip cards, for example for the identification of deliveries or products or as a means of controlling access, can be implemented particularly economically using contactless chip cards. At the same time, contactless chip cards allow a particular easy exchange of data with a reader device.
Because contactless chip cards can be read out unnoticed, security issues may arise. In particular, in access control systems, security and data protection aspects are gaining importance. In order to improve data protection, more and more data stored on a contactless chip card and data transferred from and to a contactless chip card is encrypted. The encryption and decryption is performed by a processor comprised in the contactless chip card.
Because cryptographic algorithms are particularly complex to compute, the current input is changing more rapidly during their execution than during other operations of digital circuits, for example during storing and retrieval of unencrypted data. A change in the input current of a digital circuit influences electrical variables such as the antenna voltage or impedance of the analogue circuit, such that a reception of data from a reading device may be disturbed.
In order to improve resistance to disturbance, it is known in the art to provide a decoupling circuit between the analogue circuit and the digital circuit. Such a circuit arrangement is known from the U.S. Pat. No. 6,134,130, for example. The circuit arrangement known from the art is designed to keep disturbing signals of the digital circuit away from the analogue circuit.
However, the known circuit arrangement can only ensure the desired decoupling if the antenna voltage exceeds a predefined value. Certain methods of modulation such as the so-called “Type A” transfer mode according to ISO 14443, or particular operating conditions such as large distances between a reading device and a chip card, may result in an antenna voltage too low for ensuring an effective decoupling and simultaneous demodulation of an information signal.
Consequently, it is a challenge to provide a circuit arrangement and an RFID chip card with improved communication capabilities.